Pultrusion is a known technique in which longitudinally continuous fibrous elements, which can include roving and/or mat, are collated into a structure approximating in transverse cross section the required finished cross section of the part, following which the collated fibers are soaked in a settable resin and passed through a die to effect setting of the resin into the required finished cross section defined by the die with the resin being reinforced by the fibers carried through the die with the resin.
The technique of pultrusion has been used for many years for manufacturing various parts and in more recent years has been used in the manufacture of window frames in view of the structural qualities of the finished product.
However one ongoing problem with glass fiber reinforced resin window frames of this type is that of providing a suitable finish for the product which can simulate wood which is perceived to be a higher quality product. Various attempts have been made, therefore, to apply veneers to the finished product to provide a finishing layer of wood or simulated wood to provide the required high quality finish attracted to the customer. The application of veneers is complex and expensive and thus significantly increases the cost of the product.
In prior U.S. application Ser. No. 08/327,614 filed Oct. 24, 1994, now abandoned (now published as International application W096/12611) is disclosed a technique in which a wood veneer is applied to the part during the pultrusion process so that the veneer is carried through the pultrusion die with the part as it is formed and is bonded to the part by the penetration of the resin into the interstices of the veneer. The veneer is protected on its outer surface by a covering layer so that the outside surface is intended to remain intact and of attractive appearance. However some difficulties have been encountered in preventing the penetration of the resin into the veneer sufficiently to mar the outside surface.
It is also known in pultrusion to provide a strip of a flexible carrier material which carries an abrasive or roughened surface such as fine sand which is passed with the part through the die on an outside surface of the part. The strip can then be removed from the part so that the abrasive surface is molded into the outside surface of the part and thus forms a relatively fine mat finish to the part thus avoiding the highly polished appearance which occurs normally due to the sliding action through the die. However this technique is used merely to provide a roughened or mat finish which is consistent across the full width of the area of the part required.
There remains therefore a requirement for a technique which enables a pultruded part to be formed with a wood grain finish so as to be able to simulate the high quality wood product without the necessity for attachment of veneers which are problematic.